We propose to study the mechanisms in the pituitary gland which are affected by physiological and pharmacological regulators of prolactin synthesis and release. Prolactinsecreting pituitary tumors MtTW15 and 7315a have normal dopamine receptors but are refractory to dopaminergic control of prolactin release. We will attempt to identify the post-receptor deficit in these cells. We are developing another prolactin-secreting tumor by feeding potassium thiocyanate (KSCN) to Sprague-Dawley rats and we propose to produce a similar tumor in the ACI strain of rat. We will determine the dopamine binding characteristics and biological sensitivity of these new tumors to dopamine agonists, antagonists and estradiol. These studies are designed to determine whether the low rate of prolactin synthesis by pituitary tumor cells is reversed by these agents, and whether after the anticipated increase in their in vitro release of prolactin, the cells become sensitive to inhibitory dopamine agonists. Prolactin secretion by normal pituitary cells in greatly stimulated by TRH and VIP, and we will determine whether tumor cells refractory to dopamine inhibition are similarly refractory to these peptides. We anticipate that the KSCN-tumors will be biologically responsive, demonstrating decreased prolactin release and tumor size when hosts bearing them are injected with dopamine agonists. We propose to study the effects of this treatment on the synthesis of prolactin. We will also study the DNA metabolism in experimental tumors to determine whether shrinkage of tumor mass is proportional to change in tumor DNA. We propose to determine whether factors which affect the secretion of prolactin are associated with transmethylation of phospholipids gland and pituitary tumor membranes. This will be correlated with phosphatidylinositol and phospholipid turnover studies in these tissues. Future studies are designed to determine whether phosphorylation of pituitary membrane proteins is affected by agents which influence prolactin release. Finally, studies are proposed to identify the specific dopaminergic hypothalamic nuclei activated in hyperprolactinemic rats and to correlate these changes with temporal changes in protein and LH responses in the tumor-bearing rats.